In a conventional wire electrical discharge machining apparatus, machining conditions must be previously set. It is typical that the machining conditions are provided from a machining condition table. The machining condition table ordinarily is loaded manually, by an operator input through a keyboard, and is changed in the same manner. Typically, the machining condition table is organized in accordance with applicable parameters such as workpiece materials, wire diameter, workpiece thickness, etc. There are multiple selections for each of the parameters, and an appropriate one may be selected for preventing the wire from being broken. Conditions such as taper machining and stepped workpiece machining also may be described in the machining condition tables. SKD-11, WC-Co, copper, graphite, etc. are examples of workpiece materials. .phi.0.1, .phi.0.15, .phi.0.2, .phi.0.25, .phi.0.3, etc. are examples of wire diameter. 5 mm, 10 mm, 20 mm, 30 mm, etc. are examples of workpiece thickness.
Depending on the desired machining surface roughness, there are plural machining condition patterns such as single pass machining, two pass machining, three pass machining, etc. FIG. 15 shows an example of a machining condition table for single pass machining. FIG. 16 shows an example of a machining condition table for plural pass machining. A numerical value based on applicable units is applied to each machining condition. The numerical values for a group of plural machining conditions, applicable to a given roughness, may be memorized in a numerical control unit.
The machining conditions (and an example of applicable units) may comprise the following eight factors, for example:
Vo (voltage selection): switch to select gap voltage when no load is applied (V); PA1 Ip (power setting): switch to select peak current between gaps (A); PA1 OFF (off time): switch to change off time (.mu. sec); PA1 WS (wire feeding speed): switch to adjust wire feeding speed (m/min); PA1 WT (wire tension): switch to adjust wire tension (g); PA1 LQ (dielectric fluid flow): switch to adjust dielectric fluid flow (1/min); PA1 LR (dielectric fluid resistivity): switch to adjust dielectric fluid resistivity (.OMEGA.cm); PA1 VC (average machining voltage): switch to adjust average machining voltage to a target value in machining at optimal feeding (v). PA1 a first memory for memorizing a basic machining condition group, PA1 a machining condition calling/selecting means for calling and selecting suitable machining conditions from the memory, PA1 a second memory for temporarily memorizing the machining conditions called and selected by the machining condition calling/selecting means, PA1 a third memory for memorizing machining condition changing programs, PA1 a switching means for controlling a machining condition changing function, and PA1 an operating means for changing the machining conditions temporarily memorized in the second memory by the machining condition changing programs that are stored in the third memory, according to a signal from the switching means, wherein PA1 machining is carried out according to the machining conditions changed by the operating means. PA1 a machining data memorizing means for memorizing machining data, PA1 machining data retrieving means for automatically retrieving certain machining data according to certain parameters from the machining data memorizing means, PA1 machining rule memorizing means for memorizing machining rules, and PA1 machining condition column creating means for arranging in machining order the machining data retrieved by the machining data retrieving means according to the machining rules selected according to certain parameters from the machining rule memorizing means, automatically operating parameters such as offset amount, etc. and creating machining condition columns. PA1 machining data memorizing means for memorizing machining data such as electric conditions, table moving speed, electric discharge gap, etc., PA1 machining data retrieving means for automatically retrieving certain machining data according to parameters such as wire electrodes, workpiece materials and thickness, etc. from the machining data memorizing means, PA1 machining rule memorizing means for memorizing machining rules, and
FIG. 17 is a schematic view showing the structure of a conventional wire electrical discharge machining apparatus, wherein numeral 1 denotes a wire electrode, numeral 2 denotes a workpiece, numeral 3 denotes a selection circuit, numeral 4 denotes a switching circuit (finishing machining circuit), numeral 5 denotes a resistor, numeral 6 denotes an automatic voltage regulator, numeral 7 denotes a control circuit, oscillation circuit, logic circuit, and numeral 8 denotes a machining condition setting circuit.
In the wire electrical discharge machining apparatus, voltage is applied between the wire electrode 1 and the workpiece 2, and an electric discharge pulse arises by quickly switching a power transistor in the selection circuit 3.
FIG. 18 is a schematic view of the structure of the machining condition setting circuit 8 shown in FIG. 17, wherein numeral 11 denotes a memory for memorizing a basic machining condition group, numeral 12 denotes a machining condition calling/selecting means for calling and selecting suitable machining conditions from the memory 11, numeral 13 denotes a memory for temporarily memorizing the machining conditions called and selected by the machining condition calling/selecting means 12, and numeral 17 denotes a machining means for a machining according to the machining conditions temporarily memorized in the memory 13.
Machining condition data, such as wire electrode materials and diameter, workpiece materials and thickness, and machining surface roughness, are memorized in the memory 11. Suitable machining conditions are called and selected from the memory 11 by the machining condition calling/selecting means 12, as follows. In one method, a machining condition group number is manually set by an operator using a display of a control unit, and the corresponding stored machining conditions are called from the memory 11. However, plural groups of machining conditions cannot be called at the same time by the method. When it is necessary for machining conditions to be automatically changed from current to new conditions, the following two methods are used. In one method, a machining condition group number is set in a NC program. When the program identifies a new group, the corresponding pre-stored machining conditions are called thereby. In the other method, an automatic skim cut function is used, such function being a plural pass machining of a workpiece, each machining pass being under different, predetermined, manually input conditions. Specifically, for each cut, machining parameters are input beforehand, using a display, and assigned a group number for each of the automatic skim cuts. As a result, skim cut conditions (offset, machining condition group number, and machining speed) may be automatically selected and called, and machining may be carried out. However, even though an automatic selection occurs, the conditions in each group are fixed at the values previously input by the operator and there is no ability to automatically change each condition separately.
FIG. 19 is a flow chart showing the operation of setting machining conditions in the conventional wire electrical discharge machining apparatus. A workpiece and a machining shape are determined (step S-1). Machining surface roughness is determined (step S-2). A wire electrode is selected according to workpiece thickness and minimum corner radius (step S-3). A jig is selected according to the workpiece, the machining shape, etc. (step S-4). It is judged whether a second machining pass is necessary according to the machining surface roughness, etc. (step S-5). If necessary, second machining conditions are selected (step S-6). If unnecessary, a maximum speed condition is selected (step S-7). The machining conditions, selected in step S-6 or step S-7, are set (step S-8). It is judged whether it is necessary for the machining conditions to be changed according to unusual factors (stepped workpiece machining, taper machining, etc.) (step S-9). If necessary, machining conditions according to these factors are referred to (step S-10). The machining conditions are changed by the machining data referred to (step S-11). Necessary data is selected from fifteen kinds of data for machining conditions using a machining condition group display of the numerical control unit, and the machining conditions are changed. Thereafter, or if after step S-9 if it is not necessary for the machining conditions to be changed, machining starts (step S-12). It is judged whether the machining is stable (step S-13). If unstable, or if there is a danger that the wire may be cut, for example, the machining conditions are changed in step S-11, which is repeated until the machining becomes stable.
In the conventional wire electrical discharge machining apparatus, constructed as above, machining conditions must be manually changed by an operator for economical machining or a stable machining without having the wire break. This precludes quick machining. Further, experience in operating the machine is required.
FIG. 20 is a schematic view showing a conventional wire electrical discharge machining apparatus, wherein numeral 51 denotes a wire electrode, numeral 52 denotes a workpiece, numeral 53 denotes a table, numeral 54 denotes an X-axis motor, numeral 55 denotes a Y-axis motor, numeral 56 denotes a machining power supply, and numeral 57 denotes a main control unit.
Between the wire electrode 51 and the workpiece 52, a pulse voltage from the machining power supply 56 is applied, and an electric discharge arises. The X-axis motor 54 and the Y-axis motor 55 are moved to machine desired outline shapes, being controlled by the main control unit 57. The main control unit 57 also controls the machining power supply 56. Parameters necessary for machining are the electrical conditions of the machining power supply, table moving speed, and offset amount to magnify or reduce programmed shapes, etc.
FIG. 21 shows an example of a workpiece. There are many combinations of machining surface roughness, workpiece thickness, etc. as shown in the figure. Accordingly, many machining parameters must be set for one workpiece. Machining parameters are set by the main control unit 57. Namely, machining parameters are set according to each combination of machining surface roughness, workpiece thickness, etc. in a display of the main control unit 57. 3S, 6S, and 12S in the figure denote machining surface roughnesses. 6S denotes larger roughness than 3S, and 12S denotes further larger roughness than 6S.
In the conventional wire electrical discharge machining apparatus, machining conditions are set as above, and many machining parameters must be set beforehand using the display of the main control unit 57. Accordingly, it takes much time for preparation for machining, and errors may happen. Further, it is very complicated to set many machining parameters, and the machining parameters must be set a plurality of times for one workpiece. Moreover, only a small, finite number of machining parameter combinations may be stored for selection and use. Accordingly, the machining operation is troublesome.